This invention relates to door burglar alarm systems, and more specifically relates to such systems activated or tripped by the opening motion of a door or a window.
These apparatus have been implemented by alarm systems primarily concerned with utilizing the opening of a door or window to trip a limit switch as the door or window exceeds a given limit point, whereupon an alarm signal is initiated. Such apparatus have always permitted the door or window to be opened beyond the limit point.
Many such door alarm systems have utilized cables, chains or ropes, connected between a point on the door and an alarm activation mechanism, typically, a switch control for a bell, via a pulley or guide system. Other door alarm systems have utilized a pivotal rod or hinge switch to activate an alarm. In each instance the alarm activation mechanism has permitted a complete opening of the door. The activation mechanism, whether it involved a chain or cord, a pivotal or hinged activation mechanism, or a rotating activation mechanism, has required a substantial amount of movement by the door to activate the alarm. Of necessity there has been a certain amount of "slack" or "play" designed into these systems. Such "play" was intended to compensate for the imprecise structural configuration of such systems in order to eliminate the false tripping of the alarm. "Play" was a tolerable evil necessitated by the stretching of a cable or a cord or a wearing or change in pivotal friction of a mechanical pivot trip switch.
Systems which tolerate more than a slight opening of a door provide an opportunity for detection of the existence of the burglar alarm which in turn provides the burglar with an opportunity to disarm such a system. Moreover, such systems, by the very nature of their design, exert a certain resistance to the opening of the door which resistance if detected can alert a burglar to the presence of an alarm system.
Many door alarm systems are unsightly and involve a large amount of hardware which is needed to be mounted on the interior surface of a door or on interior walls.
An object of this invention is to provide a door burglar alarm which is mountable to the door jamb and which offers no substantial resistance to the opening of the door.
A second object of this invention is to provide such an alarm which will prohibit the door from being opened beyond a certain distance.
A third object of this invention is to provide this alarm where the amount of opening can be regulated to be less than the width of the door jamb.
A further object of this invention is to provide this alarm with an activator which is movable in a plane tangent to the opening arc of the door, said plane of tangential movement by the activator providing a minimal resistance to door swing.
An even further object of this invention is to provide such an alarm having but a single mounting bracket wherein nothing is mounted to the door directly.